Solution-Processed Efficient Perovskite Nanocrystal Light-Emitting Device Utilizing Doped Hole Transport Layer

Abstract

Light-emitting devices (LEDs) with inorganic perovskite nanocrystals (PNCs) fabricated through the all-solution process have tremendous potential for new-generation illumination and displays on account of their large area and cost-effective manufacturing. However, the development of efficient solution-processed PNC LEDs remains challenge, which mainly results from the fact that only a few types of charge transport layers can be employed for the subsequent deposition steps, thus leading to injection barriers and charge injection imbalance inside these LEDs. Herein 4,4′-bis­(carbazole-9-yl) biphenyl (CBP) is introduced as a dopant into the poly­(9,9-dioctylfluorene-co-N-(4-(3-methylpropyl)) diphenylamine) (TFB) hole transport layer (HTL), which efficiently modulates the mobility of charge carrier as well as the energy level of the HTL, resulting in the barrier-free injection of the charge carrier in the as-fabricated solution-processed PNC LEDs. Consequently, the luminance of red LEDs (688 nm) reaches 2990 cd m–2, and the external quantum efficiency achieves 8.1%, which is the optimal performance for solution-processed PNC LEDs to date. Additionally, the turn-on voltage and roll-off have also been improved by the more balanced charge injection.

Bright and Efficient Pure Red Perovskite Nanocrystals Light‐Emitting Devices via In Situ Modification

“…With the modification of CaBr 2 , the electron mobility decreases as well as the hole mobility increases, giving rise to a narrower difference between electron mobility and hole mobility, which is beneficial to the balance injection of the LEDs. [ 10 ] Actually, the carrier mobilities can be increased by suppressed charge scattering with defect passivation, which is favor of the increase in charge injection efficiency and charge balance in the devices. [ 57–59 ] On the contrary, the increased ligands will reduce the carrier mobilities.…”

“…[ 1–6 ] Remarkable progress has been made to enhance the performance of PNC light‐emitting devices (LEDs) in recent years. [ 7–10 ] The external quantum efficiency (EQE) of PNC LEDs reached 23.4% for green and 23% for red, respectively. [ 11,12 ] However, the luminance of red PNC LED, especially the pure red LED with Commission Internationale de l'Eclairage (CIE) 1931 color coordinate (0.708, 0.292) from Rec.…”

Optimizing the Performance of Perovskite Nanocrystal LEDs Utilizing Cobalt Doping on a ZnO Electron Transport Layer

“…All-inorganic metal halide perovskite nanocrystals (PNCs) have become excellent candidates for next-generation displays due to their high photoluminescence quantum yields (PLQYs), tunable wavelength, and wide color gamut. − Since the first PNC LED was realized, remarkable efforts have been made to improve the LED performance. − Up to now, the external quantum efficiency (EQE) of PNC LEDs has reached 23.4% with the optimization of PNC properties and 45.5% via efficient light extraction with a hemispherical lens . Apart from the high radiative efficiency and high outcoupling efficiency, balanced carrier injection is also an essential factor for efficient PNC LEDs, , because the imbalance of electron and hole injections in the LEDs will increase the odds of Auger recombination in the emission layer (EML) and hence limit the PNC LED performance. , …”

“…To balance the carrier injection in PNC LEDs, many efforts have been made to optimize the carrier mobility of charge transport layers (CTLs) and the energy levels between different layers in PNC LEDs. ,, The most fundamental work is to select proper CTL materials according to the carrier mobility and energy level structure of the EML . Considering that ZnO can cause quantum dot quenching, and carrier injection imbalance, Yang et al chose a triazine-cored organic ETL (TmPPPyTz) to replace ZnO, which avoided quenching and realized the charge balance in the LED .…”

“…As shown in Figure e, the current density of the devices with CZO NCs decreases obviously as compared with that of the device with ZnO NCs. Moreover, the electron mobility of devices with different CZO NCs was obtained by fitting the space-charge-limited-current region (SCLC) of the curves with Child’s law where d is the thickness of ETL film (∼50 nm) and ε, ε 0 , μ, V , and J represent the relative dielectric constant, vacuum permittivity, carrier mobility, applied voltage, and current density, respectively. By assuming that ε = 4, the calculated electron mobilities of devices with different CZO films are listed in Table S3.…”